Solving the Wave Equation in Polar Coordinates

I have been using Matlab to try to numerically solve the wave equation in polar coordinates (vibrating circular membrane). I have used explicit methods and gotten consistent results. I have also tried implicit methods with inconsistent results. So, this is not a Matlab question, per se, but a math question. To wit: can someone point me to a routine or a reference that deals with the numerical solution of the wave equation in polar coordinates? Thanks.

[Yash]

http://www.giseis.alaska.edu/input/carl/research/pubs/thesis/membrane_cht_THESIS.pdf